[Tex/LaTex] Placing labels at the end of lines

pgfplotstikz-pgf

I have a display depicting two triangles that are reflections of each other across the line y=x. At the end of the line y=x – in the same direction as the line and 7.5pt away from the arrow tip – I would like to place the label $\ell$ . I tried using the following command.

\node at ($(90,90) + (45:7.5pt)$){$\ell$};

Nothing was printed – no display. I am trying to use the calc package to position the label. I guess there is some confusion because I am using the coordinate system when I issue (90,90) and I am using the pt unit when I issue (7.5pt,7.5pt).

Also, I want to have k and $k^{\prime}$ typeset at the end of the two other lines drawn in the display. The slopes of the lines are 1/3 and 3. So, I would like to put these labels off the right arrow tips of these lines – in the same direction as the line and 7.5pt away from the arrow tip. (I think that the "added space" would be issued using {atan(1/3):7.5pt} or {atan(3):7.5pt}.)

\documentclass{amsart}
\usepackage{amsmath}

\usepackage{tikz}
\usetikzlibrary{calc,angles,positioning,intersections}


\usepackage{pgfplots}
\pgfplotsset{compat=1.11}


\begin{document}


\begin{tikzpicture}
\begin{axis}[width=5in,axis equal image,clip=false,
axis lines=middle,
xmin=-54,xmax=90,
xlabel=$x$,ylabel=$y$,
ymin=-54,ymax=90,
restrict y to domain=-54:90,
enlargelimits={abs=0.25cm},
axis line style={latex-latex},
ticklabel style={font=\tiny,fill=white},
xtick={\empty},ytick={\empty},
extra x ticks={15},
extra x tick labels={15},
xticklabel style={anchor=south},
xticklabel shift=-4pt,
extra y ticks={15},
extra y tick labels={15},
yticklabel style={anchor=west},
yticklabel shift=-4pt,
xlabel style={at={(ticklabel* cs:1)},anchor=north west},
ylabel style={at={(ticklabel* cs:1)},anchor=south west}
]

\addplot[dashed,latex-latex,samples=2,domain=-54:90]{x};

\draw (axis cs:-30,-30) coordinate(A) node[left]{$A$};
\draw (axis cs:-21,29) coordinate(B) node[above left]{$B$};
\draw (axis cs:18,42) coordinate(C) node[above]{$C$};
\draw (axis cs:0,15) coordinate(P);

\addplot[dashed,latex-,samples=2,domain=-54:-21,blue]{(1/3) * x + 36};
\addplot[dashed,-latex,samples=2,domain=18:90,blue]{(1/3) * x + 36};

\draw (axis cs:29,-21) coordinate(b) node[below right]{$B^{\prime}$};
\draw (axis cs:42,18) coordinate(c) node[right]{$C^{\prime}$};
\draw (axis cs:15,0) coordinate(p);

\addplot[latex-,samples=2,loosely dash dot,domain=18:29,green]{3 * x - 108};
\addplot[-latex,samples=2,loosely dash dot,domain=42:66,green]{3 * x - 108};

\draw [fill] (54,54) circle [radius=1.5pt];
\end{axis}

\draw[blue] (A) -- (B) -- (C) -- cycle;
\draw[dashed,blue] (B) -- (P);


\draw[dashed,green] (A) -- (b) -- (c) -- cycle;
\draw[densely dashed,green] (b) -- (p);

\end{tikzpicture}

\end{document}

Best Answer

Using the calc library you can say

( $ (A)!<length>!(B) $ )

to locate the point that is <length> units from (A) on the segment joining (A) and (B). For example

\node at ( $ (axis cs:90,90)!7.5pt!(axis cs:100,100) $ ) {$\ell$};

will place $ell$ at a distance 7.5pt away from (axis cs:90,90) along the segment joining (axis cs:90,90) and (axis cs:100,100).

The code:

\documentclass{amsart}
\usepackage{amsmath}

\usepackage{tikz}
\usetikzlibrary{calc,angles,positioning,intersections}


\usepackage{pgfplots}
\pgfplotsset{compat=1.11}


\begin{document}


\begin{tikzpicture}
\begin{axis}[width=5in,axis equal image,clip=false,
axis lines=middle,
xmin=-54,xmax=90,
xlabel=$x$,ylabel=$y$,
ymin=-54,ymax=90,
restrict y to domain=-54:90,
enlargelimits={abs=0.25cm},
axis line style={latex-latex},
ticklabel style={font=\tiny,fill=white},
xtick={\empty},ytick={\empty},
extra x ticks={15},
extra x tick labels={15},
xticklabel style={anchor=south},
xticklabel shift=-4pt,
extra y ticks={15},
extra y tick labels={15},
yticklabel style={anchor=west},
yticklabel shift=-4pt,
xlabel style={at={(ticklabel* cs:1)},anchor=north west},
ylabel style={at={(ticklabel* cs:1)},anchor=south west}
]

\addplot[dashed,latex-latex,samples=2,domain=-54:90]{x};
\node at ( $ (axis cs:90,90)!7.5pt!(axis cs:100,100) $ ) {$\ell$};

\draw (axis cs:-30,-30) coordinate(A) node[left]{$A$};
\draw (axis cs:-21,29) coordinate(B) node[above left]{$B$};
\draw (axis cs:18,42) coordinate(C) node[above]{$C$};
\draw (axis cs:0,15) coordinate(P);

\addplot[dashed,latex-,samples=2,domain=-54:-21,blue]{(1/3) * x + 36};
\addplot[dashed,-latex,samples=2,domain=18:90,blue]{(1/3) * x + 36};

\node at ( $ (axis cs:90,0.3333*90+36)!7.5pt!(axis cs:100,0.3333*100+36) $ ) {$k$};

\draw (axis cs:29,-21) coordinate(b) node[below right]{$B^{\prime}$};
\draw (axis cs:42,18) coordinate(c) node[right]{$C^{\prime}$};
\draw (axis cs:15,0) coordinate(p);

\addplot[latex-,samples=2,loosely dash dot,domain=18:29,green]{3 * x - 108};
\addplot[-latex,samples=2,loosely dash dot,domain=42:66,green]{3 * x - 108};

\node at ( $ (axis cs:66,3*66-108)!7.5pt!(axis cs:100,3*100-108) $ ) {$k'$};

\draw [fill] (54,54) circle [radius=1.5pt];
\end{axis}

\draw[blue] (A) -- (B) -- (C) -- cycle;
\draw[dashed,blue] (B) -- (P);


\draw[dashed,green] (A) -- (b) -- (c) -- cycle;
\draw[densely dashed,green] (b) -- (p);

\end{tikzpicture}

\end{document}

The result:

enter image description here

For consistency's sake and also to facilitate code maintenance, you could define some functions:

\documentclass{amsart}
\usepackage{amsmath}

\usepackage{tikz}
\usetikzlibrary{calc,angles,positioning,intersections}


\usepackage{pgfplots}
\pgfplotsset{compat=1.11}


\begin{document}


\begin{tikzpicture}[
declare function={ 
  line1(\x) = (1/3) * \x + 36;
  line2(\x) = 3*\x - 108;
  }
]
\begin{axis}[width=5in,axis equal image,clip=false,
axis lines=middle,
xmin=-54,xmax=90,
xlabel=$x$,ylabel=$y$,
ymin=-54,ymax=90,
restrict y to domain=-54:90,
enlargelimits={abs=0.25cm},
axis line style={latex-latex},
ticklabel style={font=\tiny,fill=white},
xtick={\empty},ytick={\empty},
extra x ticks={15},
extra x tick labels={15},
xticklabel style={anchor=south},
xticklabel shift=-4pt,
extra y ticks={15},
extra y tick labels={15},
yticklabel style={anchor=west},
yticklabel shift=-4pt,
xlabel style={at={(ticklabel* cs:1)},anchor=north west},
ylabel style={at={(ticklabel* cs:1)},anchor=south west}
]

\addplot[dashed,latex-latex,samples=2,domain=-54:90]{x};
\node at ( $ (axis cs:90,90)!7.5pt!(axis cs:100,100) $ ) {$\ell$};

\draw (axis cs:-30,-30) coordinate(A) node[left]{$A$};
\draw (axis cs:-21,29) coordinate(B) node[above left]{$B$};
\draw (axis cs:18,42) coordinate(C) node[above]{$C$};
\draw (axis cs:0,15) coordinate(P);

\addplot[dashed,latex-,samples=2,domain=-54:-21,blue]{line1(\x)};
\addplot[dashed,-latex,samples=2,domain=18:90,blue]{line1(\x)};

\node at ( $ (axis cs:90,{line1(90)})!7.5pt!(axis cs:91,{line1(91)}) $ ) {$k$};

\draw (axis cs:29,-21) coordinate(b) node[below right]{$B^{\prime}$};
\draw (axis cs:42,18) coordinate(c) node[right]{$C^{\prime}$};
\draw (axis cs:15,0) coordinate(p);

\addplot[latex-,samples=2,loosely dash dot,domain=18:29,green]{line2(\x)};
\addplot[-latex,samples=2,loosely dash dot,domain=42:66,green]{line2(\x)};

\node at ( $ (axis cs:66,{line2(66)})!7.5pt!(axis cs:67,{line2(67)}) $ ) {$k'$};

\draw [fill] (54,54) circle [radius=1.5pt];
\end{axis}

\draw[blue] (A) -- (B) -- (C) -- cycle;
\draw[dashed,blue] (B) -- (P);


\draw[dashed,green] (A) -- (b) -- (c) -- cycle;
\draw[densely dashed,green] (b) -- (p);

\end{tikzpicture}

\end{document}

Related Solutions

[Tex/LaTex] How to hide empty (value 0) ybars with pgfplots

You can use

 y filter/.expression={y==0 ? nan : y}

in the options of \addplot.

\documentclass{article}

% ---------------------------------- tikz
\usepackage{pgfplots}          % to print charts
\pgfplotsset{compat=1.12}

\begin{document}

\begin{figure}
  \centering
  \begin{tikzpicture}
    \begin{axis} [
      % general
      ybar,
      scale only axis,
      height=0.5\textwidth,
      width=1.2\textwidth,
      ylabel={\# Dots},
      nodes near coords,
      xlabel={Variation},
      xticklabel style={
        rotate=90,
        anchor=east,
      },
      %enlarge x limits={abs value={3}},
      ]
      \addplot+[y filter/.expression={y==0 ? nan : y}] table [
        x=grade,
        y=value,
      ] {
grade   value
-11 0
-10 0
-9  0
-8  0
-7  0
-6  0
-5  3
-4  1
-3  2
-2  15
-1  11
0   179
1   8
2   1
3   0
4   1
5   2
6   0
7   0
8   0
9   0
10  0
11  0
      };
    \end{axis}
  \end{tikzpicture}
\end{figure}
\end{document}

[Tex/LaTex] Line up nested tikz enviroments or how to get rid of them

As is explained in How do I draw shapes inside a tikz node? pics can be used for defining new objects. My main problem using pics is how to place where you want because they aren't nodes and positioning them is not so easy.

Following code shows how to define EDFA block.

    EDFA/.pic={
        \begin{scope}[scale=.5]
        \draw (-1,0) coordinate (in) --  (-1,1) -- (1,0) coordinate (out) --  (-1,-1) -- cycle;
        \node[anchor=north,inner sep=2pt] at (0,-1) {$1$};
        \end{scope}

In this case, coordinate (-1,0) will act as west anchor and 1,0 as east. Both point will have an special name for further reference. Every pic is placed according its own origin (0,0). You can use Claudio's answer to Anchoring TiKZ pics for better positioning.

As your example was simple, I'd prefer to star with EDFA and place Source and Sink after it.

\documentclass[]{article}

% tikz
\usepackage{tikz}
\usetikzlibrary{positioning} %relative positioning

\begin{document}

\tikzset{%
    EDFA/.pic={
        \begin{scope}[scale=.5]
        \draw (-1,0) coordinate (in) --  (-1,1) -- (1,0) coordinate (out) --  (-1,-1) -- cycle;
        \node[anchor=north,inner sep=2pt] at (0,-1) {$1$};
        \end{scope}
    }
}

\begin{tikzpicture}[
block/.style={draw},
]

\draw pic (edfa) {EDFA};

\node[block, left=of edfain] (source) {Source};

\node[block, right= of edfaout] (sink) {Sink};

\draw[->] (source) -- (edfain);
\draw[->] (edfaout) -- (sink);

\end{tikzpicture}

\end{document}

I understand that your components are more complex than EDFA because for this particular case an isosceles triangle node with a label will do the work and it can be used as a node and not as a pic:

\documentclass[]{article}

% tikz
\usepackage{tikz}
\usetikzlibrary{positioning} %relative positioning
\usetikzlibrary{shapes.geometric}

\begin{document}

\begin{tikzpicture}[
    block/.style={draw},
    edfa/.style={isosceles triangle, minimum width=1cm, 
         draw, anchor=west, isosceles triangle stretches, 
         minimum height=1cm, label=-80:#1}
]

\node[block] (source) {Source};

\node[edfa=1, right=of source] (edfa) {};

\node[block, right= of edfa] (sink) {Sink};

\draw[->] (source) -- (edfa);
\draw[->] (edfa) -- (sink);

\end{tikzpicture}

\end{document}

Best Answer

Related Solutions

[Tex/LaTex] How to hide empty (value 0) ybars with pgfplots

[Tex/LaTex] Line up nested tikz enviroments or how to get rid of them

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